1. Field of the Invention
This invention relates to a hovering tone arm for a recording playback apparatus particularly a hovering linear tone arm tracking system for a recording playback apparatus.
2. The Prior Art
In the recording playback industry linear tone arm tracking systems are well known for their tracking accuracy in view of their structural similarity to the linear stylus that cuts the record master as compared with the more common pivotable tone arm which must swing in an arc across a recording and a built-in tracking error results. Accordingly, linear tracking playback systems for recordings are inherently more accurate than their pivotable counterparts and such linear systems are enjoying increasing demand from hi-fi (and stereo) fans.
Such linear tracking pickup and playback systems have been the subject of several U.S. patents. In the earlier systems a stylus arm would ride directly on a rail powered by a small servo motor which was designed to compensate for the friction of the system and to shift (the pivot end of) the tone arm to correspond with the shift of the stylus as it radially traversed the grooves of a rotating record. However, difficulties in synchronizing the servo motor with the shift of the stylus led to development of the floating or hovering tone arm, which rides above a linear rail in response to groove pressures on the tracking stylus, eliminating the need for a servo motor. Accordingly, the tone arm friction is reduced to that of moving the tone arm through the air.
The above development has been the subject of several U.S. patents, e.g. U.S. Pat. No. 3,479,038 to Eisner, U.S. Pat. No. 4,087,095 to Koda and U.S. Pat. No. 3,771,797 to Braun.
The first two patents, Eisner and Koda, disclose a linear tracking system wherein a tone arm is connected to a sleeve which surrounds and rides on an air cushion emitted by an air-bearing tube. The tube is positioned parallel to a turntable radius so that the stylus moves radially on a record. Such surrounding sleeves have a drawback in that they require a considerable amount of air pressure to maintain a clearance all the way around the support tube or rail and accordingly require a relatively large compressor to maintain such sleeve in a hovering, low friction position, cross-sectionally speaking.
The full or enclosing sleeve adds considerable weight to the tone arm, requiring considerable air pressure to keep such assembly suspended, as discussed above. Then there is a tolerance problem, for should the sleeve shift in any direction, it can contact the rail or air-bearing tube, introducing friction and immediate stress and distortion to the playback system.
The Braun reference discloses a permanent-magnet guideway which receives a permanent magnet guide piece or tone arm carriage, the guide piece being held in a hovering position in the guideway by magnetic forces. As shown in FIG. 3 of the Braun reference, the guide piece, while disclosed as hovering in the guide channel, is held captive within the confines thereof and has limited sectional rotational movement, which lack requires the tone arm to be suspended below the guide piece on a pivot. Thus, the tone arm and guide piece assembly cannot readily be removed from such guideway.
Accordingly, in the prior art linear tracking systems which have a hovering carriage on a guide rail, all three are held relatively captive sectionally on such rail, cannot be lifted directly off such rail, except at the ends thereof, and have considerable weight which requires considerable supporting forces, either gaseous or magnetic.
Accordingly, in a linear tracking recording playback system there is a need and market for a tone arm carriage and guideway assembly that obviates the above prior art shortcomings.
There has now been discovered a tone arm carriage and guideway assembly for a linear tracking system for a recording wherein the carriage is light-weight, readily hovers above the guideway and instead of being captive on such guideway, readily sectionally pivots thereon and lifts off such guideway at any desired point. Further, the tone arm carriage rides or hovers over the linear guideway on a gas bearing or, in another embodiment, on a magnetic bearing.